Swift Fuels 100R, GAMI G100UL, and the future of tetraethyl lead (TEL)
The references below were current as of mid-August 2026. Reporting on the TEL production timeline conflicts, and the most recent item is a statement from Innospec itself that no firm end date has been set. Check the sources for later developments.
In July 2026 the FAA added more than 1,200 engine models and 1,600 airframe models to the Approved Model List for Swift's 100R STC. Swift says these Phase I approvals cover aircraft that burn up to 56% of the 100LL sold in the US, with higher-performance engines expected in Phase II and Phase III during 2026, 2027, and early 2028.
100R meets ASTM D8603, and owners who bought Swift's UL94 STC receive a 100R STC at no charge. Swift expects airports now selling UL94 to begin switching to 100R, with participating locations in 29 states, including Minnesota and Wisconsin. Swift also plans to begin seeking an airport grant-assurance waiver in October 2026, with large-scale deployments following in 2027.
G100UL holds an Approved Model List STC covering nearly all spark-ignition piston engines and airframes, but it has reached few airports. GAMI's availability map lists two locations in California plus airports in Mississippi and Texas, short of the national availability GAMI had earlier projected for 2026.
In August 2026 GAMI applied for an ASTM specification for G100UL, and ASTM accepted George Braly's request to form a task force to review the fuel. Some California operators have reported fuel leaks and staining. GAMI's position is that nearly every aircraft it examined had already been leaking 100LL. Owners should review the published guidance on older nitrile O-rings and tank sealants before switching fuels.
Innospec is the only recognized producer of the tetraethyl lead used in 100LL. What has been reported about when it will stop making TEL has changed over time:
As of the most recent source, a TEL end date of 2028-2030 has been reported but not confirmed by the manufacturer.
On the regulatory side, an FAA official declined in July 2026 to commit to the 2030 date. The FAA's July 30, 2026 transition plan still targets 2030 and requires airports to keep 100LL available while unleaded fuels become more widely available.